In the fields of industrial/consumer equipments and electric appliances, synthetic resins are widely used as they are excellent in processability, chemical resistance, weatherability, electrical properties and mechanical strength as compared with other materials, and also the amount of synthetic resins used has been increasing. However, since synthetic resins have flammability, it is required to impart flame retardancy and the required performances have gradually enhanced recently. Therefore, a halogen-containing compound or a mixture of a halogen-containing compound and an antimony compound such as antimony oxide, as a conventional flame retardant, is added to a resin composition, for example, an epoxy resin composition used in an encapsulant and a substrate of electronic components such as LSI (Large Scale Integration) so as to impart flame retardancy. However, the resin composition containing such a flame retardant may generate a halogen-based gas which may cause environmental pollution upon combustion or molding. Also, the halogen-based gas may inhibit electrical properties and mechanical properties of electronic components. Thus, as a flame retardant for synthetic resin, non-halogen-based flame retardants which are less likely to generate a halogen-based gas upon combustion or molding, for example, metal hydrate-type flame retardants such as aluminum hydroxide and magnesium hydroxide, and phosphorous-type flame retardants such as phosphate-type flame retardants, condensed phosphate-type flame retardants, phosphoric amide-type flame retardants, ammonium polyphosphate-type flame retardants and phosphazene-type flame retardants, are widely used.
Among these flame retardants, metal hydrate-type flame retardants must be used in a large amount to a resin composition so as to enhance the flame-retardancy, although they exert the flame-retardant effect by that an endothermic reaction of dehydration thermolysis and release of water thereby occur in the same temperature range as that of thermolysis or combustion initiation of the synthetic resin. Therefore, a molded article of a resin composition containing this kind of a flame retardant has a drawback that a mechanical strength decreases. Meanwhile, among phosphorous-type flame retardants, phosphate-type flame retardants and condensed phosphate-type flame retardants have drawbacks that the mechanical strength of the resin molded article decreases when a large amount of flame retardants are added to the resin composition so as to enhance flame retardancy because they have a plasticizing effect. As for phosphate-type flame retardants, phosphoric amide-type flame retardants and ammonium polyphosphate-type flame retardants, it is substantially difficult to use them in materials for production of resin molded articles to which long-term mechanical and electrical reliability is required as they are likely to be hydrolyzed. In contrast, phosphazene-type flame retardants have widely been used as an effective flame retardant for the synthetic resin, as described in the documents 1 to 5 below, since they exert less plasticizing effect and has less hydrolyzability as compared with other phosphorous-type flame retardants, and thus the amount of them to be added to the resin composition can increase. However, when the amount of the phosphazene-type flame retardants to be added to the resin composition is increased, reliability of the resin molded article at high temperature may deteriorate. Specifically, in the case of a thermoplastic resin-type resin composition, phosphazene-type flame retardants are likely to bleed out (leak out) from the resin molded article at high temperature. In the case of a thermosetting resin-type resin composition, deformation such as blister of the resin molded article may occur at high temperature and a short-circuit may be caused thereby when the resin molded article is used as a laminated substrate or the like in electronic and electric fields.
Document 1
Japanese Unexamined Patent Publication (Kokai) No. 2000-103939
Document 2
Japanese Unexamined Patent Publication (Kokai) No. 2004-83671
Document 3
Japanese-Unexamined Patent Publication (Kokai) No. 2004-210849
Document 4
Japanese Unexamined Patent Publication (Kokai) No. 2005-8835
Document 5
Japanese Unexamined Patent Publication (Kokai) No. 2005-248134
Thus, an improvement of the phosphazene-type flame retardants is studied so as to enhance reliability of the resin molded article at high temperature (thermal reliability). For example, documents 6 to 10 below disclose phosphazene-type flame retardants having a reactive group such as a hydroxyl group, and epoxy resin and polyimide resin compositions using them. Even if a large amount of these phosphazene-type flame retardants are added to the resin composition, thermal reliability of the resin molded article is less likely to deteriorate. However, phosphazene-type flame retardants are insufficient in a required essential result of effectively enhancing flame retardancy of the resin molded article even if the amount is increased, and also deteriorate mechanical properties (particularly, high glass transition temperature) of the resin molded article.
Document 6
Japanese Unexamined Patent Publication (Kokai) No. 6-247989
Document 7
Japanese Unexamined Patent Publication (Kokai) No. 10-259292
Document 8
Japanese Unexamined Patent Publication (Kokai) No. 2003-302751
Document 9
Japanese Unexamined Patent Publication (Kokai) No. 2003-342339
Document 10
Japanese Unexamined Patent Publication (Kokai) No. 2004-143465
With recent size reduction and achievement of higher function of electronic equipments, substrate materials, which are thin and lightweight and also capable of achieving higher density wiring, are required for printed circuit boards. As a printed circuit boards, build-up laminated type of small size with an IVH (Interstitial Via Hole) structure, in which only required layers are connected by way of non-through holes, have rapidly been developed. As for an insulating layer of a printed circuit board of the build-up laminated type, a heat-resistant resin having high glass transition temperature (Tg) is required to be used instead of a base material such as a glass fabric.
In computers and information equipment terminals, an increase in frequency of signal is promoted so as to process much data at higher speed. However, there is a problem that transmission loss of electrical signal increases as the frequency increases, and it is strongly required to develop printed circuit boards suitable for higher frequency signal. Dielectric loss determined by dielectric properties of an insulating layer (dielectric) in the vicinity of a wiring exerts a large influence on transmission loss in a high frequency circuit, and it becomes necessary to achieve low dielectric constant and low dissipation factor (tan δ) of a substrate for a printed circuit board (particularly insulating resin). For example, in equipments relating to a mobile communication, a substrate having low dissipation factor is strongly required so as to decrease transmission loss in a quasi-microwave band (1 to 3 GHz) with the increase of frequency of signal.
Furthermore, in electronic information equipments such as computers, a high-speed microprocessor having operating frequency of more than 1 GHz is mounted and there arise a problem such as delay of high-speed pulse signal in a printed circuit board. Since delay time of signal increases in proportion to square root of a relative dielectric constant ∈r of an insulator in the vicinity of a wiring in a printed circuit board, a substrate for a circuit board having low dielectric constant is required in high-speed computers.
Therefore, it is necessary for phosphazene-type flame retardants to scarcely cause deterioration of dielectric properties of the resin molded article, that is, to achieve low dielectric constant and low dissipation factor of the resin molded article.
Thus, an object of the present invention is to realize a phosphazene compound which can effectively enhance flame retardancy without deteriorating mechanical properties of a resin molded article, and is also less likely to deteriorate thermal reliability and dielectric properties of the resin molded article.